Wrathall Mark wrote:

The Boeing 777 has a Maintenance Access terminal along the same lines.
Gives the fault code, the unit detecting the fault, the suspect
components in order of probability, number of times fault occurred and
flight phase. Using the fault code you use a fault isolation manual
which also takes cost into account (ordering up wiring checks before
FADEC replacement for example). Problem with the engine is that the
sensors are almost all analog with the A/D conversion taking place in
the FADEC. So most every engine problem lists component, wiring, FADEC,
as the FADEC detects all faults. Due to the low power (5-20v, milliamps
) contaminated pins on connectors are some of the most common causes. We
also have some systems where a stack up of tolerances can cause
intermittent faults. At least you almost always have faults isolated to
a single sensor system before you start. The fact that all sensors are
dual channel also helps. If one channel fails a valve yet the valve is
in the commanded position and the second channel agrees, you can save a
lot of money avoiding valve replacement. That sounds kind of lame that
the GM system doesn't even give it's own technicians enough clues to
prevent shotgun troubleshooting.
                    Mark Wrathall
                  Lauda Air
                   Production, Planning and Control
                GE90 Powerplant Engineer
             * + 43 1 7000-75320
           Fax +43 1 7000-75315

 
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